The invention is related to that of U.S. Pat. No. RE.30,403, the disclosure of which is hereby incorporated by reference herein.
The invention relates generally to controls for industrial fluid control systems, and especially for pneumatic systems in which a reciprocable fluid motor is shifted between two positions by way of a four-way control valve or the like. Conventionally, such pneumatic systems have a three-way supply valve in the pressurized air supply line for feeding the control valve, with the supply valve being shiftable to its exhaust position in order to evacuate the system, and then later shifted back to its supply position for system operation. In some systems, this can result in sudden and potentially dangerous shifting of the controlled device Such a controlled device can be a press, for example, which can drift by gravity or by inadvertent external forces to one position when line air is depleted and then be suddenly shifted back to another position when full line pressure is applied.
It is known in the art to provide a piston-actuated, poppet safety valve between the supply and control valves, with such a safety valve being spring-urged to its closed position, but having a restricted bypass from the supply valve to both the piston chamber and outlet ports of the safety valve. With this arrangement, full air pressure will be initially prevented from flowing from the supply valve to the control valve when the former is opened, but instead will slowly build up in the safety valve actuating piston chamber and simultaneously on one side of the reciprocable fluid motor, thus slowly and safely shifting the motor to its opposite position. When the piston chamber pressure reaches a predetermined value, the safety valve will fully open and provide full supply pressure to the control valve for normal operation.
In some versions of such a safety valve, the flow restriction is in the form of a narrow hole drilled in the poppet valve member itself, with a restricted housing passage leading from the outlet port to the piston chamber. This prior construction has disadvantages, such as requiring the drilling of a separate hole in each poppet valve. Thus it has been found to be quite difficult to obtain satisfactory results in obtaining the right size of restriction, since extreme accuracy is required. Furthermore, in such a construction, it is impossible to vary or adjust the restriction size once the hole is drilled through the poppet valve member, with such adjustability often being very desirable.
These disadvantages were previously overcome and avoided by an improved safety valve described and disclosed in the previous U.S. Pat. No. RE.30,403, which is assigned to the same assignee as the present invention, with the disclosure of such patent being incorporated by reference herein. The invention of this patent provided a novel and improved safety valve construction for fluid systems of the type described, but which is more simple, economical, and convenient to construct. It further provided an improved safety valve that permitted convenient adjustability of its speed of operation.
The invention of such previous patent was adapted for use in combination with a compressed air supply line for a reciprocable fluid motor, with the supply line having a supply valve for selectively pressurizing and exhausting the supply line and a control valve for controlling the fluid motor. The safety valve was interposed between the supply and control valves, with the safety valve having a housing, supply and outlet ports in the housing, and a radial valve seat in the housing. A valve stem carrying a poppet valve member was engageable with the valve seat, and a spring urged the member against the valve seat, with an actuating piston being connected to the valve stem and movable within a piston chamber opening to one face of the housing. The piston chamber was enclosed by a cover on the housing face, with a first passage leading from the supply port to a portion of the piston chamber formed by the cover, with a second passage leading from this portion of the piston chamber to the outlet port, and with an adjustable restriction in the first passage. The relative dimensions of the piston and the spring were such that the piston would shift the valve member against the urging of the spring to its open position when a predetermined proportion of the full line pressure was reached.
In one embodiment of such previous invention, the adjustable restriction included a threaded portion in the first passage, adjacent the housing face, and a plurality of externally threaded plugs alternately and interchangeably mountable in the threaded portion, with the interchangeable plugs having restricted passages of various minimum diameters. In another version of such previous invention, the adjustable restriction was accomplished by way of a needle valve rotatably mounted in the cover and disposed within a portion of the first passage, whereby rotation of said needle valve in a flow orifice served to easily adjust the restriction size.
An improved safety valve according to the present invention includes piston-actuated provisions for gradually pressurizing the fluid motor during start-up of the system, preferably by way of a changeable flow restriction in a manner generally similar to that of the safety valve disclosed and described in the above-mentioned U.S. Pat. No. 30,403. In addition, however, such improved safety valve preferably includes a floating exhaust valve actuating apparatus movable in an exhaust closure chamber and that operates in response to the presence or absence of line pressure in the exhaust closure chamber for respectively blocking off or opening fluid communication between the safety valve's outlet port and exhaust port. A pilot operator is also included in the safety valve assembly in at least one embodiment of the invention for selectively permitting or cutting off line pressure flow to actuate the piston actuator and the exhaust valve actuating apparatus. Such pilot operator can alternately, however, be provided upstream of the safety valve inlet or supply port. The preferred safety valve also includes a check valve for preventing back-flow from the safety valve's outlet port back to the piston actuator and back to the exhaust valve actuating apparatus.